We use the following definitions:
- Extent of occurrence (EOO; as defined by the IUCN) is the general
region a species occurs in, including all known, inferred or projected
sites. It is calculated as the area of a convex hull around the whole
distribution- basically a polygon around the whole range. EOO reflects
large or small distribution.
- Area of Occurence (AOO) is the area within its EOO which is actually
occupied by a taxon. It is calculated as the area of the sum of grid
cells a species occurs in. AOO reflects how often you find the species
within its large distribution
- Wide-ranging species have an EOO > 20 000
km2 following IUCN’s Criterion B1 or are present in
> ⅓ of a country’s 20-km grid squares (following Katayama
et al. 2014 in PLoSOne).
- Restricted species are those with an EOO < 20 000
km2 or an AOO < 2 000
km2. A list of restricted species compiled using KBA
criteria (i.e.IUCN Criteria B2) can be found online fromhttps://www.keybiodiversityareas.org/working-with-kbas/proposing-updating/criteria-tools;
however, it is recognized that not all restricted species will be
included in this list.
- Rare species must meet at least one of the three criteria (see
Rabinowitz 1981):
- Restricted range: EOO <500 km2, OR
- Habitat specialist: restricted to a specialized microhabitat so that
it has a very small AOO (typically smaller than 20
km2), OR
- Low densities of individuals: always occurs as single individuals or
very small subpopulations (typically fewer than 50 mature
individuals) scattered over a wide area
In addition, we ask if the species is naturally (historically) rare or
recently rare due to anthropogenic influences (i.e., threats) (Q70).